Rotation limit device



April 14, 1970 R. M, FORD ETAL 3,505,884

ROTATION LIMIT DEV-ICE Filed June 5, 1968 \\l 1. f 30 nvvewroe ROBERT M.FORD oawo m FRIDAY if 82W 3 AGE/VT United States Patent O 3,505,884ROTATION LIMIT DEVICE Robert M. Ford and David W. Friday, Framingham,

Mass., assignors to Raytheon' Company, Lexington, Mass., a corporationof Delaware Filed June 3, 1968, Ser. No. 733,893 Int. Cl. F16h 35/18 US.Cl. 74-10.2 5 Claims ABSTRACT OF THE DISCLOSURE.

A knob mounted on the end of a rotatable shaft which extends through acontrol panel from an adjustable device supported on the rear side ofthe panel, the knob having a circular series of equally spaced holes inthe panel side thereof, two of said holes containing removable pinswhich protrude from the panel side of the knob to define the maximumlimits of clockwise and counterclockwise rotation of the knob. Ananti-rotate washer orientates the adjustable device on the control paneland has a right angle tab which extends out from the control panel intothe rotational path of the roll pins which protrude from the panel sideof the knob.

BACKGROUND OF THE INVENTION This invention relates generally to knobsfor control devices and, more particularly, is concerned with anadjustable means for selecting the desired limits of clockwise andcounterclockwise rotation of the knob.

The operation of equipment today is controlled, to a great extent, byadjustable devices, such as valves, rheostats, potentiometers, variablecapacitors, gang switches and the like. Generally, these devices aremounted in a control panel on the rear side thereof and have a rotatablecontrol shaft which extends through a hole in the panel to protrude fromthe front side thereof. A knob is mounted on the end of the shaft and isattached thereto in binding fashion, such as by journalling a radiallyextending screw in the knob against a flat surface on the shaft of thecontrol device. Thus, turning the knob rotates the shaft and varies thesetting of the adjustable device.

Since some of the commercially available control devices allowcontinuous rotation of the control shaft, a problem arises when limitsmust be set on the rotational adjustment of the control device.Instances occur where an operator can exceed critical limits and causedamage to the associated operating equipment. For example, the entireoutput of a potentiometer, applied across the terminals of a circuit,could be excessive and burn out valuable components in the circuit. Inmany cases, when the control device is provided with rotational limits,the stoppingmechanism is located internally in the body of the device,which is often potted. Control devices of this type do not provide meansfor adjusting the maximum limits of rotation to conform with thecritical limits required by the associated operating equipment.

One solution disclosed by the prior art provides a control knob having afixed extension tab which will strike an object protruding from thecontrol panel in the rotational path of the tab. Usually, screws or thelike are installed in the control panel to engage the extension tab atthe selected limits of clockwise and counterclockwise rotation. However,this solution does not provide a convenient means for adjusting thelimit stops. If a change in the location of the limit stops is required,the only alternative is to drill additional holes in the panel so thatthe screws or like objects may be installed at the newly selected pointsof maximum rotation.

3,505,884 Patented Apr. 14, 1970 Therefore, the solution to this problemnot only requires a means to limit the rotation of the control knob butalso a means for adjusting the location of the limit stops should achange of this type be required by the associated operating equipment.Furthermore, the change in maximum rotation should be accomplishedeasily and quickly; therefore the means of adjusting the limit stopsshould be readily accessible to the operator.

SUMMARY OF THE INVENTION In accordance with these objectives, thisinvention provides a control knob having a circular series of equallyspaced cavities in the panel side thereof, two of the respective holescontaining respective removable pins which protrude outwardly from thepanel side of the knob and an anti-rotate washer having a right angletab which extends into the rotational path of the aforementioned pins.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing may be more fullyunderstood from the description when read together with the accompanyingdrawing wherein:

FIG. 1 is an exploded, perspective view partly in axial section of thepreferred embodiment of this invention;

FIG. 2 is an. elevational view, partly in axial section, of thepreferred embodiment of this invention; and

FIG. 3 is an axial sectional view taken along lines 3-3 of FIG. 2looking in the direction of the arrows.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing,wherein like characters of reference designate like parts throughout theseveral views, there is shown in FIGS. 1 and 2 an adjustable controldevice 10, such as a potentiometer for example, which is mounted in acontrol panel 12 from the rear side thereof. The rotatable shaft 14 andthreaded collar 16 of control device 10 extend through a hole 18 inpanel 12 and protrude from the front side thereof. An antirotate washer20 is placed over collar 16 and has a radial, inwardly extending, tab 22which fits into a longitudinal slot 24 on the outer diameter of thecollar 16 and a right angle tab 26 which extends rearwardly into a hole28 in panel 12. Thus, the anti-rotate washer 20 orientates the body ofcontrol device 10 with respect to the panel and prevents the device fromturning when the shaft 14 is rotated. A nut 30 is journalled onto thethreaded collar 16 to hold the body of control device 10 and theanti-rotate washer 20 tightly against the panel 12. As shown in FIG. 3,cavity 35, centrally located in the panel side of control knob 32,receives and slidingly engages the end of the rotatable shaft 14. Knob32 is bindingly attached to a shaft 14 by any convenient means, as byjournalling a screw 34 into a radially disposed hole 33 in knob 32 untilscrew 34 bears against the flat surface of a landing 36 on shaft 14.Thus, turning the control knob 32 rotates the shaft 14 and varies thesetting of control device 10.

Since the entire output of the control device 10., such as apotentiometer for example, may damage the operating equipment associatedwith it, maximum limits of clockwise and counterclockwise rotation ofthe shaft 14 are required. As shown more clearly in FIG. 3, the panelside of knob 32 is provided with a circular series of equally spacedcavities 40. A removable spring pin 42, protruding from the rear orpanel side of knob 32, is press-fitted into a cavity 40 which cavity islocated at the selected limit of clockwise rotation of knob 32. Anotherremovable spring pin 42 similarly carried by knob 32, is press-fittedinto another cavity 40, which cavity is located at the selected limit ofcounterclockwise rotation of knob 32. When one of the pins 42 is engagedby an object which extends outwardly from panel 12 and into therotational path of the pins 42, rotation of the knob 32 will be stopped.One method of providing a fixed stop is shown in the drawing andcomprises a tab 44 which extends outwardly or forwardly from theantirotate washer and protrudes into the rotational path of the pins 42.Rotation of the knob will be stopped in either the clockwise orcounterclockwise direction when the respective pin 42 strikes againstthe tab 44. Thus, the pins 42 in knob 32 and tab 44 on anti-rotatewasher 20 determine the maximum clockwise and counterclockwise movementof control knob 32. Accordingly, the arcuate distance between pins 2determines the maximum rotary movement of shaft 14 and, consequently,the variable range of control device 10.

The rotary movement of the control knob 14 can be increased or decreasedby loosening the set screw 34 and sliding the knob 32 off the end ofshaft :14 whereupon the spring pins 42 can be removed from the cavitiesinto which they have been press-fitted and reinstalled into othercavities which conform more closely to the newly selected limits ofmaximum clockwise and counterclockwise rotation. The pins 42 can beremoved entirely if continuous rotation of the shaft 14 is desired. Theknob is replaced on the end of the shaft 14, the set screw 34 in knob 32is tightened and the control device is back in operation in a very shorttime, with rotary movement of the shaft 14 restricted to the new limitsof maximum rotation. Having the adjustable means on the knob 32 is amost convenient arrangement because the knob is the closest element ofthe assembly to the operator and is the first unit removed in gainingaccess to any other element of the assembly.

Although fifteen cavities are shown in the circular series on the panelside of the knob in FIG. 3, it is apparent that the number of holescould be increased or decreased as required by the associated operatingequipment. Although right angle tab 44, extending outwardly from theanti-rotate washer, provides the illustrated positive limit stop, otherfixed means would function as well, such as a screw journalled into thepanel. The arrangement of this invention would not require moving thescrew to change the limits of rotation of the knob because theadjustable feature of the invention is located on the panel side of theknob. Although the knob has been shown attached to a rotatable shaft bymeans of a radially disposed screw, the knob may be attached by othermeans, such as press-fitting it onto the end of the rotatable shaft.These and other modifications which may occur to those skilled in theart are within the spirit and scope of this invention.

We claim:

1. A control knob having a panel side with a central opening locatedtherein for receiving an end of a rotatable shaft and a circular seriesof equally spaced holes radially spaced from said central opening, andtwo pins interfitting into respective holes of said circular series andprotruding from the panel side of the knob, said pins being removablefrom said holes and reinsertable in other selected holes of saidcircular series.

2. A control knob attached to an end of a rotatable shaft protrudingfrom a panel, said knob having in the panel side thereof a series ofuniformly spaced holes concentric with the rotatable shaft, at least oneof said cavities carrying a removable member which protrudes from thepanel side of the knob, and fixed stop means located in the rotatationalpath of said member for defining the maximum limit of rotation of saidknob.

3. A control knob as set forth in claim 2 wherein said fixed stop meansincludes an anti-rotate washer fixedly attached to the panel, and a tabextending outwardly from said washer.

4. In combination, a control knob bindingly attached to one end of arotatable shaft, said shaft protruding from a panel and extendingthrough a hole in the panel to an adjustable device mounted on theopposite side of the panel, said knob having in the panel side thereof acircular series of equally spaced cavities radially spaced from therotatable shaft, two pins, each having an end disposed within arespective cavity and having an opposite end extending outwardly fromthe panel side of the knob, said pins being removable from saidrespective cavities and insertable into other respective cavities of thecircular series, and an anti-rotate washer between said panel and knoband having a portion thereof interlocked with said device, anotherportion interlocked with the panel, and a tab extending outwardly fromthe panel into the rotational path of said pins, thereby defining themaximum limits of clockwise and counterclockwise rotation of said knob.

5. A control knob having a rear side with a central opening forreceiving a shaft therein, spaced holes in said rear side of the knoband radially spaced from said central opening, said holes being greaterthan two in number, and two members in two of said holes and projectingoutwardly from said rear side of the knob, said members being removablymounted in said holes for reinsertion in other selected holes asdesired.

References Cited UNITED STATES PATENTS 2,444,485 7/1948 Aitcheson 74-5533,214,985 11/1965 Danek et al 74-526 X MILTON KAUFMAN, Primary ExaminerUS. Cl. X.R. 74526

